Chicago Air quality today

What is ozone smog, and how much does Chicago get?

Ozone at ground level is a harmful gas and the main ingredient in smog ^[4]. It is not given off directly. It forms when pollution from cars, power plants, industrial boilers, refineries and chemical plants reacts in sunlight ^[4]. It is most likely to reach unhealthy levels on hot, sunny days in cities ^[4].

In the Lung Association's 2026 report, the Chicago-Naperville area had 18 unhealthy ozone days a year, down from 20.3 in the 2025 report ^[1]. It ranked 15th worst of 226 metro areas, and Cook County had the area's worst ozone grade, an F ^[1].

What is PM2.5, and how much does Chicago have?

PM2.5 means fine particles 2.5 micrometers across or smaller. A human hair is about 30 times wider than the largest of them ^[6]. Among particles, these pose the greatest risk to health ^[6]. Most particle pollution forms in the air from chemicals given off by power plants, industries and cars ^[6].

In the 2026 report, the Chicago-Naperville area ranked 13th worst of 211 metro areas for year-round particle pollution ^[1]. Cook County had a failing grade, with levels above the federal standard ^[1]. The area also averaged 3.7 days a year with unhealthy short-term spikes in particle pollution ^[1].

How does wildfire smoke reach Chicago?

On June 27, 2023, smoke from wildfires in Canada pushed Chicago's air into the very unhealthy range, according to Illinois EPA monitors ^[2]. The state issued an Air Quality Alert, and the city moved park district camps, public school activities and other events indoors where possible ^[2].

In June 2025, northern winds carried smoke from wildfires in central Canada down to Chicago, and the city's air ranked among the worst in the world ^[3]. The state issued an air pollution action day for Cook and seven nearby counties ^[3].

Wildfire smoke can travel long distances, so fires hundreds of miles away can affect Illinois air ^[5]. In July 2026, Illinois officials warned that smoke could reach northern Illinois while the Chicago region was already under an ozone alert ^[5]. The biggest health threat from smoke comes from its fine particles ^[7].

What is being done about Chicago's air?

Illinois EPA posts a daily forecast using the Air Quality Index, or AQI, a color scale from green for good to maroon for hazardous ^[5]. When the Chicago area is forecast to reach orange, unhealthy for sensitive groups, for two or more days in a row, it calls an Air Pollution Action Day ^[5]. These days ask residents and businesses to cut their own pollution ^[5].

During the June 2023 smoke, the city urged people to limit driving and refueling and asked employers to allow working from home where possible ^[2]. When the 2026 report came out, the Lung Association's advocacy director urged Illinois leaders to pass the Hazel M. Johnson Cumulative Impacts Ordinance in Chicago and to back state laws curbing warehouse pollution ^[1].

How to protect yourself in Chicago

Check the daily AQI forecast each morning, as Illinois EPA advises, especially if you have asthma or another lung disease ^[5]. When the air is bad, children, older adults, people with breathing problems and anyone active outdoors are most at risk ^[5]. Choose shorter or less intense outdoor activities, take more breaks, or reschedule ^[5]. Ozone is most likely to be high on hot, sunny days ^[4].

When wildfire smoke arrives, stay indoors with windows and doors closed, and set an air conditioner with a fresh air intake to recirculate ^[5]. Portable air cleaners and high-efficiency furnace or air conditioning filters, such as those rated MERV 13, can remove smoke particles indoors ^[7]. Avoid making more particles inside, such as by smoking or burning candles ^[5].

If you must be outside in smoke, consider a high-quality N95 mask, which filters fine particles ^[5]. If symptoms such as wheezing, chest pain or shortness of breath get worse, call your doctor or 911 ^[5].